Best sound and playability ever in a shooter - the explosions make my room vibrate, unbelievable!

And originality - playing the jeep means you will not be hit by the flying things (most of the enemies fly) so that is easier, BUT you have to dodge all the buildings, use bridges, jump over obstacles, be careful at the train crossing etc.

And then in the water, the jeep becomes a boat and there's all this inertia suddenly that makes it slide... wow! All this makes the background interactive. And really the background becomes a major factor in the whole experience, making you feel like actually being in that world!

Also it had really imaginative bosses, like the giant stationary laser cannon!

The makers of swiv figured out what I think is the secret to fun in shmups: Give the player many small enemies that are blasted each by just ONE HIT. Then make the game harder by simply dumping more enemies and faster enemies at the player. Most shooters make the mistake of confronting the player with enemies that each take at least two shots to kill. That is too slow, and much less fun! And that is why silkworm and swiv still stand out for me as the most fun shmups ever!

It is just hard enough to be fair and possible, but still so damn HARD!
Graphics have incredible pixel perfect attention to detail. Explosions with little pixel perfect rotating pieces of shrapnel flying everywhere just make it fun to blast away at them.
It's just great old school fun with none of these stupid complicated zen-like rule and point systems like Ikaruga. Those zen things are too complicated for me. I just want to shoot. I think a shooter should be about survival and not about collecting score, a shmup is not a pinball game after all! pffh...